Glass fiber friction element

ABSTRACT

A friction disc comprises continuous longitudinally co-extensive generally parallel glass strands wound spirally in the plane of the disc; short, generally parallel glass strands extending normal to the plane of the disc along said spiral; non-ferrous metal chips or wires; and a heat curable cement binding said glass strands and non-ferrous metal chips or wires together. The friction disc is made by forming a glass fabric with warp rovings of continuous parallel glass strands and fill rovings of continuous parallel glass strands; impregnating the fabric with a heat curable cement; winding the glass fabric onto a mandrel to form a spirally wrapped cylinder; slicing the cylinder into disc preforms; and molding the disc preforms under heat and pressure. Either non-ferrous metal wires are included in the fabric or non-ferrous metal chips are deposited on the fabric prior to wrapping the fabric onto the mandrel.

This is a division of application Ser. No. 252,119, filed May 10, 1972,now U.S. Pat. No. 3,870,581.

BACKGROUND OF THE INVENTION

The present invention relates to friction elements such as clutchfacings and the method of making such elements utilizing woven glassfiber rovings as the reinforcing and friction material.

Conventional clutch facings for automotive service employ asbestos yarnand a non-ferrous wire like copper, brass, or zinc which are twistedtogether, treated with a friction cement, wound into preforms, moldedand finished. As spin strength requirements for clutch facings becamemore demanding, glass fibers were used to strengthen the facings whileretaining asbestos fibers for the friction material. However, it was notuntil the inventions disclosed in application Ser. No. 156,267 filedJune 24, 1971, now U.S. Pat. No. 3,756,910 and Ser. No. 156,410 filedJune 24, 1971, now U.S. Pat. No. 3,743,069 that glass fibers were usedwith non-ferrous metal and cement to provide a friction element withglass fibers as both the reinforcing and friction material.

It is an object of the present invention to provide an improved frictionelement which has excellent spin strength and frictional properties. Itis a further object of the present invention to provide a method ofproducing such a friction element from woven glass fiber rovings whichis faster and more economical than previous methods employed.

The improved friction element is achieved by providing a disc havingcontinuous, untwisted parallel strands of glass fiber extending in acircumferential direction in the disc to provide the required spinstrength. The friction element also has strands of glass fiber extendingin a direction that is generally normal to the face of the disc toprovide excellent frictional properties. The disc is either providedwith non-ferrous metal chips which are dispersed throughout the disc ornon-ferrous metal wires which are included in the circumferentiallyand/or normally extending strands of the disc.

The improved method of forming the friction element comprises forming aglass fabric of continuous parallel glass warp strands and continuousparallel glass fill strands; passing the fabric through a bath of heatcurable cement to impregnate the fabric; winding the fabric onto amandrel to form a spirally wrapped cylinder; slicing the cylinder intodisc preforms; and molding said disc preforms under heat and pressure.Non-ferrous metal is incorporated into the friction element by eitherdepositing non-ferrous metal chips on the fabric prior to wrapping thefabric on the mandrel or including non-ferrous metal wires in the warpand/or fill strands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of apparatus for carrying out themethod of the present invention;

FIG. 2 is a perspective view illustrating an apparatus for slicing thecylinder into disc preforms;

FIG. 3 is a diagramatic perspective of a friction element preform of thepresent invention such as a clutch facing preform, with portions brokenaway to illustrate the orientation of glass strands within the preform;and

FIG. 3a is an enlarged view of that portion of the clutch facing shownin FIG. 3 as a broken away section.

FIG. 4 is a face view of a friction element of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4 illustrates a friction element 20, e.g., a clutch facing, of thepresent invention made in accordance with the method of the presentinvention. The friction element 20 is a disc with an inner annular edge22, a peripheral annular edge 24 and substantially flat annular frictionsurfaces 26 extending intermediate edges 22 and 24. The friction element20 is made up of long continuous spirally wound glass strands 28 whichlie in planes generally parallel to the surface 26 of the disc and shortglass strands 30, located throughout the disc, which extend between andare normal to surfaces 26. The orientation of the strands within thedisc is best shown in FIG. 3a which represents the friction elementpreform prior to the molding operation.

In one embodiment non-ferrous metal chips 32 such as brass, copper, orzinc chips are uniformily interspersed with the glass fiber strands 28and 30 with a friction cement binding the glass strands and non-ferrousmetal chips together. In another embodiment, non-ferrous fine metalwires 34 such as brass, copper or zinc wires are included with the shortstrands 30 and extend intermediate faces 26 of the clutch facing in adirection substantially normal to the surfaces 26. As with the otherembodiment, friction cement holds the glass strands and non-ferrous wireelements together.

It is also contemplated that fine metal wires 34 can be included withthe spirally wound glass strands 28 either in conjunction with wiresincluded with the short strands 30 or as an alternative to the placementof wires with the short strands. However, the purpose of the wires 34 orchips 32 is to provide a source of non-ferrous metal which is dispersedover the surface 26 of the disc during operation to prevent or minimizechatter. The non-ferrous metal is also thought to act as an inorganicfriction material which is stable at high temperatures and as a means tohelp dissipate heat during use of the disc. With the wires included inthe spirally wound glass strands 28, the amount of wire exposure mightvary greatly during different phases of disc wear thereby providing anonuniform supply of non-ferrous metal for dispersion over the surface26. Thus it is preferred to include the wires with the short strands 30where their ends will always be exposed to provide a more uniform sourceof non-ferrous metal for surfaces 26 and consequently a disc withrelatively constant performance characteristics throughout its use.

While various heat curable cements can be used for the binder, apreferred binder is a rubber phenolic friction cement. A typical rubberphenolic friction cement, in approximate percentages by weight totaling100% comprises: GRS Polymer 30%; Curing Agents 30%; Fillers 20%; andResin 20%.

FIGS. 1 and 2 illustrate apparatus for carrying out the method of thepresent invention. A fabric 38 of woven glass fiber rovings is unwoundfrom a supply roll mounted on a mandrel 40, impregnated in a bath 42,dried in a drying tower 44, wrapped on a mandrel 46, sliced into discsby slicing apparatus 48 and molded into the final product. Whennon-ferrous metal chips 32 are included in the friction element, thechips are deposited on the fabric 38 by a distributing apparatus orhopper 50.

The fabric 38 of woven glass fiber rovings comprises warp rovings 52 andfill rovings 54. The rovings each contain 10 to 120 ECK glass strands.Each strand is made up of 200 to 800 individual continuous ECK glassfilaments which each have a diameter in the range of about 12 to 14microns. Each warp roving 52 is continuous with the individual strands28 making up each warp roving being continuous from one end of theroving to the other end of the roving. Likewise, each fill roving 54 iscontinuous with the individual strands 30 making up each fill rovingbeing continuous from one end of the roving to the other end of theroving. The strands in each of the rovings are substantially parallelwith respect to each other with little or preferrably no twist beingpresent.

When non-ferrous metal chips 32 are not going to be included in thefriction element 20 the fine metal wires 34 are included in the warpand/or fill rovings. The fine metal wires 34 are in parallel alignmentwith the glass strands of the respective roving and are continuous fromone end of the roving to the other.

According to the method of the present invention a roll of fabric 38which is to be treated according to the process of the present inventionis first mounted on a mandrel 40. The mandrel is rotatably mounted inbearings and is free to rotate about its longitudinal axis as the fabric38 is drawn off the supply roll. The impregnating bath 42 is provided tothoroughly impregnate the fabric with a heat curable cement such as arubber phenolic friction cement. The bath 42 comprises a reservoir 56and a pair of idler rolls 58 and 60 which direct the fabric down intoand through a pool 62 of the friction cement. The idler roll 60 ismounted beneath the surface of the cement pool 62 to thereby assure thatthe fabric 38 is immersed in the pool for a sufficient length of time tobe thoroughly impregnated with the cement.

The squeeze rolls 64 are mounted on parallel axes with the fabric 38passing intermediate the rolls. Means such as hydraulic cylinders 66 areprovided to adjust the spacing between the rolls so as to vary thepressure exerted on the fabric by the rolls. This enables the rolls tobe correctly adjusted to control the amount of cement impregnation.While squeeze rolls 64 are shown, it is also contemplated that othermeans could be utilized to remove excess cement from the fabric such asa pair of roll and knife assemblies.

The drying tower 44 is generally about 25 feet in height. The towerincludes a pair of idler rolls 68 and 70 rotatably mounted so as toguide the fabric through the tower. The tower is electrically heated byheating units 72 or steam heated to the desired temperature foreffecting the removal of volatiles from the cement and is provided withan exhaust fan 74 to remove the volatile vapors from the tower. Thelength of travel of the fabric through the tower; the rate at which thefabric is drawn through the tower; and the temperatures within thedrying tower are regulated so that the volatiles will be removed fromthe cement without causing the cement to set prematurely.

The hopper 50 is provided to distribute the non-ferrous metal chips 32over the surface of the coated fabric prior to wrapping the fabric onthe mandrel 46. While many different types of apparatus can be employedto evenly distribute the non-ferrous metal chips over the material,hopper 50 is provided with a screw or auger 76 which extends the lengthof the hopper and feeds the non-ferrous metal chips 32 through alongitudinally extending slot 78 in the bottom of the hopper. The bottomplate 80 of the hopper 50 is slidably mounted on the hopper so that thewidth of the slot can be adjusted. The amount of non-ferrous metal chipsdistributed onto the fabric can be regulated by adjusting the rotationalspeed of the auger and/or the opening of the discharge slot 78 in thebottom of the hopper.

The mandrel 46 is driven by a motor 82 or other conventional means todraw the material from the supply roll through the impregnating bath 42,the squeeze rolls 64, the drying tower 44 and onto the mandrel. Thefabric is spirally wrapped on the mandrel to form a hollow cylinder 84of the coated fabric 38. Due to the relatively slow speed at which thefabric 38 is wound on the mandrel 46, the motor 82 is coupled to themandrel through a speed reducer 86. A coupling 88 connecting the speedreducer to the mandrel is a conventional releasable coupling to allowthe mandrel to be removed once the winding is completed. If the fabricis subjected to excess stresses or tension some of the idlersillustrated in the apparatus can be replaced by powered rolls tofacilitate the feed of the fabric from the supply roll to the mandrel46. However, a certain amount of tension must be maintained on thefabric 38 as it is being wrapped onto mandrel 46 to assure that thefabric is tightly wound about this mandrel. Preferably the mandrel 46has an outside diameter which is substantially equal to the desiredinside diameter of the preform. In this way the final machining of theproduct after molding is minimized.

The mandrel is adapted to fit on a slicing apparatus 48 as shown in FIG.2. There the mandrel is rotated by the motor 90 which is connected tothe mandrel by a releasable coupling 92. While the mandrel is rotated, aknife 94, or other similar means slices the cylinder into discs of thedesired thickness. A conventional assembly, not shown, is provided tofeed the knife 94 toward the mandrel to effect a cut, retract the knifewhen a cut has been completed and then index the knife 94 longitudinallywith respect to the mandrel for the next cut.

After the slicing is completed, the disc like preforms, illustrated inFIG. 3, are removed from the mandrel. Due to the friction betweenadjacent and overlapping layers of strands resulting from the windingoperation plus the inherent tackiness of the uncured cement composition,the disc preform 20 maintains its disc-like form. The uncured preform isthen placed between flat platens under pressure in the range of 2,000 to2,500 psi and cured at a temperature of from 320°F to 340°F for 4minutes. This initial cure hardens resins to a non-flow condition.Thereafter the partially cured and densified preforms are removed andsubjected to a post bake for completing the polymerization of theresins. The post bake comprises further curing under reduced pressurefor about 6 hours at 360°F and 2 hours at 400°F. Upon completion of thispost cure, the discs are ready to have flashing removed and be ground tothe proper thickness. The finished facings in FIG. 4 are provided withrivet holes having counter bores for reception of attaching rivets forsecuring the facings to a clutch plate or brake mounting not shown.

What we claim is:
 1. A friction element consisting essentially of anannular disc of glass strands bonded together with a cement, said dischaving an inner annular edge, an outer annular edge, and generally flatsurfaces extending intermediate said edges, said disc having one portionof said glass strands extending spirally from said inner edge to saidouter edge and the other portion of said strands extending normal tosaid flat surfaces and dispersed throughout said disc.
 2. The frictionelement as defined in claim 1 wherein a non-ferrous metal isinterspersed with said glass strands.
 3. The friction element as definedin claim 2 wherein said non-ferrous metal is selected from a groupconsisting of brass, copper or zinc.
 4. The friction element as definedin claim 2 wherein said non-ferrous metal is in the form of chipsinterspersed with said glass strands.
 5. The friction element as definedin claim 2 wherein the non-ferrous metal is in the form of strandsinterspersed with said glass strands extending normal to said flatannular surfaces.
 6. The friction element as defined in claim 1 whereinsaid cement is a rubber phenolic friction cement.
 7. The frictionelement as defined in claim 1 wherein said glass strands are continuous.